117841-07-3Relevant academic research and scientific papers
Efficient Diastereoselective Syntheses of erythro- Or threo-a-Alkyl-β-hydroxy Sulfones by Reductions of α-Alkyl-β-keto Sulfones with TiCI4/BHg or LiEtsBH/CeCl3, Respectively
Marcantoni, Enrico,Cingolani, Simone,Bartoli, Giuseppe,Bosco, Marcella,Sambri, Letizia
, p. 3624 - 3630 (2007/10/03)
A stereoselective synthesis of erythro- and threo-α-alkyl-β-hydroxy sulfones by reduction of the corresponding α-alkyl-β-keto sulfones has been developed. The pivotal role in this methodology is played by the chelating or nonchelating properties of the Lewis acid employed. The strong chelating TiCl4 led to the erythro isomer in high diastereomeric excess in noncoordinating solvents (CH2Cl2) at -78 °C using BH3/py as reducing agent, while the nonchelating CeCl3 gave a high excess of the threo isomer in coordinating solvents (THF) at the same temperature using lithium triethylborohydride (LiEt3BH) as reducing agent. Moreover, this methodology has been successfully utilized for the synthesis of α-allyl-β-hydroxy sulfones, which are useful synthetic intermediates to obtain 2,5-disubstituted tetrahydrofurans by electrophilic cyclization.
Stereochemical studies on the formation of α,β-epoxysulfones using α-chloro-β-hydroxysulfones of known configuration
Grossert, J. Stuart,Sotheeswaran, Subramanian,Dharmarante, H. Ranjith W.,Cameron, T. Stanley
, p. 2870 - 2879 (2007/10/02)
Substitution reactions adjacent to sulfonyl groups are known to proceed with difficulty, and there is evidence to suggest that these may not necessarily proceed by an SN2 pathway.The mechanism of these reactions could be studied in principle by using the conversion of α-chloro-β-hydroxysulfones of known configuration into α,β-epoxysulfones of known configuration.This paper describes results in which this has been attempted.However, the stereochemical aspects of the epoxide formation could not be assigned unequivocally because of the intervention of a very facile "retro-aldol" process when the chlorohydrins are subjected to treatment with bases, although the experimental results do suggest that the reaction does proceed in a regular SN2-like manner, with inversion at carbon.The X-ray crystal structures of two highly substituted α,β-epoxysulfones are presented, thus putting the structures, including stereochemistry, of a range of these compounds of firm ground.
Steric effects in the diastereoselective reduction of β-ketosulfones
Grossert, J. Stuart,Dharmaratne, H. Ranjith W.,Cameron, T. Stanley,Vincent, Beverly R.
, p. 2860 - 2869 (2007/10/02)
The stereochemical course of the reduction of ketones adjacent to a chiral center normally shows some diastereoselectivity (described by Cram's rule), the degree of which is dependent on the structure of the ketone and on the reaction conditions; the selectivity in acyclic species is often not very great.In this paper, we described the sodium borohydride reduction of four acyclic β-ketosulfones, containing a chiral center at the α-position, in which the products are formed with high diastereoselectivity.Reasons for this selectivity became apparent when we were able to show that these ketosulfones apparently exist predominantly in the same conformation in solution as in the solid state.This conformation requires that the preferred trajectory for nucleophilic attack on the carbonyl group leads to reaction on the re face, to yield the threo diastereomer of the β-hydroxysulfone.The results that led to these conclusions were obtained from stuctural studies by X-ray crystallography, as well as by detailed 1H and 13C nuclear magnetic resonance spectroscopy.In some cases, the latter spectra were run both in solution and in the solid state.
